Concept:Federalism in Nigeria was introduced through the constitutional changes of 1946.
Explanation:Before 1939, Nigeria was administered as a single unit.
Sir Bernard Bourdillon, the Governor-General then, created separate provincial groupings to reflect regional differences.
His successor, Sir Arthur Richards, later formalised this division into a federal system.
This arrangement became known as the Richards Constitution of 1946.
Therefore, that constitution is credited with introducing federalism in Nigeria.
Answer:A. Richard's Constitution